Add information/warning about outdated versions in the ontology documentation

[lcomet]

Currently we are showing the webpage and also allowing download of previous versions of the ontology.
Adopt similar approach as other ontologies/vocabularies specifications' websites
For reference see: https://www.w3.org/TR/2019/PR-vocab-dcat-2-20191119/

[JohannesLipp]

Thank you for raising this! After speaking with @clange , we suggest the following:

Instead of a invasive popup notification, we suggest a lightweight/simple text warning somewhere in the version area (in red, if you like):

You could update existing HTML updates in the pipeline (which use the sed tool IIRC) to simply insert a warning there. Thank you!